Measurement and Dimensional Analysis

The Importance of Measurement A.Measuring is a fundamental skill of science. B.Without measurements we could not describe our observations.

Measurements provide a standard. A.Two types of measurement 1.Quantitative measurements- give results in a definite form, usually as numbers. ex: “The car weighs 2000 kg.” 2.Qualitative measurements- give results in a descriptive nonnumeric form. ex: “The car is blue.”

The Metric System A. Although the United States still uses the English system of measurement, the rest of the world has switched to a standard form of measurement known as the metric system.

What metric units do you know? A.Give a metric unit of measurement for the following quantities: 1.Mass 2.Temperature 3.Volume 4.Time

Base Units in the Metric System A.Base units are defined based on something observable object or event in the world 1. length- meter(m) 2. mass- gram(g) 3. time- second(s) 4. electric current – ampere(A) 5. temperature – celsius (C) 6. amount of substance – mole (mol) 7. luminous intensity – candela (cd)

Derived Units in the Metric System A.A derived unit is a combination of base units, and sometimes other derived units 1.Volume: Liter (L) a)1 L = 1000ml = 1000 cm3 2.Density: grams per cubic centimeter ( g/cm3 ) 3.Force: Newton (N) = 1 kg m/s 2 4.Energy: joule (J) = 1Nm

Using Measuring Tools in Science A.You must always read the scales on equipment one place past the last mark.

Examples A.What is the volume of the following liquids.

A.Determine the mass of the object on the balance.

Measuring Matter Mass 1.Measurement of the quantity of matter in an object 2.Ex) golf ball = mass = 45 g, tennis ball = 2.5 g Density 1.Mass and volume can be used to find density 2.D = m/v 3.Ex) mass = 10 g volume = 2 cm 3 10 g = 5 g/cm 3 2 cm 3

Measuring Distance Length 1.Distance between two points 2.Ex) diameter of a hair, distance from Earth to the Moon 3.SI unit length = meter (m) 4.The unit for measure depends on what you are measuring a)Ex) cm – pencilm – classroomkm – school to home b)By choosing appropriate units you avoid large digit numbers

Measuring Volume Volume 1.amount of space occupied by an object 2.v = l x w x h a)Multiply 3 numbers and units together b)Ex) a cube 3 cm length, 3 cm width, 3 cm height i.3 cm x 3 cm x 3 cm = 9 cm 3 Liquid volume 1.Can’t actually measure size of water but measure the container it is in 2.Liquid volume units = liter (L) or milliliter (mL)

Measuring Time and Temperature Time – interval between 2 events 1.SI unit – (s) seconds Temperature – a measure of how hot or cold something is (thermal energy) 1.Celsius ( o C) – body temp – 37 o C room temp – 20 o C freezing point – 0 o Cboiling – 100 o C 1.Kelvin (K) – 0 K is coldest possible temperature freezing point – 273 Kboils – 373 K o C = K – 273K = o C + 273

Converting within the metric system A.Although the basic units are sufficient for most measurements, many times it is necessary to talk about amounts so big, or so little that the numbers would be hard to understand if they were reported in m,g,or l.

Converting Within the Metric System

Conversion Factor A.Conversion factors (a ratio that is equal to one) are used to change one unit to another 1.Ex) 1000 mL in 1 L mL = mL = 1L = 1 1 L 1L 1L 1. 1L = mL

kilogram (kg) --- gram (g) --- pound (lb) --- ounce (oz) --- meters (m) miles (mi) --- centimeters (cm) --- feet (ft) --- gallon (ga) --- liters (L) inch (in) --- second (s) --- minute (min) --- hour (hr) --- milliliter (mL) kilometer (km) --- day (day) --- fluid ounce (fl oz) 1 mile = 5,280 feet --- 1,600 meters = 1 mile pound = 16 ounces 1 kilogram = 2.2 pounds inch = 2.54 centimeters ounce = grams 1 gallon = 3.79 liters fluid ounces = 1 gallon 1,000 grams = 1 kilogram 1,000 milliliters = 1 liter --- 1,000 meters = 1 kilometer

Understanding size in metric conversions A.Which is larger 1m or 1cm? B.Which is smaller 1km or 1dm?

Practice Converting Units A.Convert 1m to cm.

A.How many grams are in 1.25 kg?

A.Convert l to microliters.

Combining Skills A.Which is bigger 1m or 100mm? B.Which is smaller 3.25km of 3,250m?

Converting Using Dimensional Analysis A.Many times it is necessary to convert from one unit to another using an equality: 1.Equations a)Ex: Converting Celsius to Fahrenheit 2.Fractional a)Converting Metric to English

Examples A.Convert cm to inches

A.Convert 12.8m to inches

A.Convert 7 weeks into seconds